1. Field of the Invention
The present invention relates to an exhaust timing control system and control unit. More particularly, the present invention relates to an exhaust timing control system and control unit of a snowmobile.
2. Description of Related Art
Snowmobiles are powered by internal combustion engines, particularly two stroke engines. Additionally, small snowmobiles do not have batteries to power electrical accessories when the engine is not operating; such accessories are powered by a generator when the snowmobile engine has been started. Larger snowmobiles may have batteries; however, due to the unusually cold operating environments that these vehicles are subjected to, the batteries may store and retain little power.
The conventional two stroke engines which power snowmobiles generally include an exhaust port provided in each cylinder wall such that spent gases are exhausted through the exhaust port as the piston reciprocates in the cylinder. Exhaust port timing has an important effect on engine performance. Optimum exhaust port timing is dependent, in part, upon engine speed. For instance, to provide an improved engine performance, the exhaust port timing can be advanced during high-speed engine operation relative to the exhaust port timing during engine idling.
One manner of controlling the exhaust port timing is to employ exhaust control valves. Generally, these valves are of the sliding or rotating type, and do not serve to ever completely close the opening or port in each combustion chamber. Instead, each valve moves between a first position, in which the valve does not obstruct, or obstructs very little of, the exhaust port, and a second position, in which the valve partially obstructs the port. Therefore, the exhaust control valve can alter the effective cross-sectional area of the exhaust port by appearing to lower an upper surface of the exhaust port, thereby restricting the flow through the exhaust port.
Because these valves have a relatively small range of movement, and are not continuously moved, they may seize within the guide passage in which they are mounted. Such seizure may result due to deposits that form on the valve bodies. Specifically, because these valves are normally employed in two cycle engines and because oil is typically mixed with the air and fuel charge ported into the combustion chamber, the oil can cause a further problem once the engine is shut off. While the engine is running, the engine temperature will be high enough to avoid any carbonization of the oil byproducts on the valves. However, as a stopped engine cools, residual oil may carbonize, or coke, on the control valves and form deposits which, along with other foreign matter, will make it difficult to operate the valves when the engine is later restarted. In short, these deposits will tend to inhibit smooth operation of the valves. Of course, the aforementioned temperature differences will also further aggravate this situation.
In the past, it has been suggested to exercise the exhaust control valve through a number of cycles between an opened and a closed position to clean any scale, carbon deposits or other debris from the exhaust control valve. In vehicles having sufficient battery power, the control valves are cycled through a cleaning operation under power from the battery before the engine is started. However, in a vehicle such as a snowmobile, which does not have a battery, a cleaning operation may not occur prior to starting.
Additionally, movement of the exhaust control valves typically alters engine performance characteristics such that efficiencies may be obtained at a lower engine speed range without significantly harming engine performance at a higher engine speed range. For instance, closing the exhaust control valves delays the timing of the exhaust cycle such that the compression ratio is increased. This increase enhances low speed engine performance. Again, due to the cold environment in which snowmobiles are used, the cold starting temperature of the engine typically causes difficulties when starting the engine. Moreover, the cold temperature can result in rough idling and rough engine running at low speed.
One aspect of the present invention recognizes that maintaining the exhaust control valve in an open position during shutdown affords some advantages in cold environment vehicles. For instance, opening the valves by retracting them offers a final cleaning operation to remove deposits that may later coke on the valve bodies. Accordingly, the valves a less likely to stick on a subsequent restart if the valves are cycled to an open position on shutdown in vehicles not have a battery to power the valves in a cleaning cycle prior to such a subsequent restart.
Accordingly, it is desired to have a snowmobile having an exhaust control valve control which performs a cleaning operation upon shutdown under the power of an electrical generator and which returns the valves to an open or retracted position upon engine shutdown. Additionally, it is desired to have a snowmobile which employs a mapped positioning control of the exhaust control valves such that engine performance can be enhanced at a low end while substantially maintaining high end good high end performance.
In accordance with the present invention, there is provided a snowmobile comprising an engine driving a track. The engine having a crankshaft and a combustion chamber. An exhaust port leading from the combustion chamber for routing exhaust products therefrom and an exhaust valve cooperable with the exhaust port. The exhaust valve being movable between a first position for delaying the closing of the exhaust port and a second position for advancing the closing of the exhaust port. The snowmobile further comprising an electrical power source that generates power through a connection to the engine crankshaft, a control unit powered by the electrical power source and a drive control in communication with the control unit. The drive control being capable of moving the exhaust valve at least partially between the first position and the second position. The control unit signaling the drive control to extend the valve from the first position to the second position if the engine has an engine speed within a predetermined range. The control unit signaling the drive control to retract the valve from the second position to the first position if the engine speed is outside of the predetermined range, wherein the predetermined range has a lower limit engine speed below which the electrical power source cannot generate sufficient energy the supply to power control unit.
Another aspect of the present invention involves a snowmobile comprising an engine driving a track. The engine has an output shaft, a combustion chamber, and an exhaust port leading from the combustion chamber for routing exhaust products therefrom. An exhaust valve is cooperable with the exhaust port and is movable between a first position for delaying the closing of the exhaust portion and a second position for advancing the closing of the exhaust port. The engine further comprises an electrical power generator that is connected to the output shaft to generate electrical energy. The snowmobile also has a control unit and a drive control in electrical communication with the control unit. The drive control and the control unit receive power from the electrical power generator. The drive control is capable of moving the exhaust valve at least partially between the first position and the second position. The control unit activates the drive control to cycle the exhaust valve between the first position and the second position in a cleaning operation before the engine attains a first predetermined speed, wherein the first predetermined speed is below an idle speed.
Yet another aspect of the present invention involves a method of conducting an exhaust timing control valve cleaning operation. The method comprises sensing an engine speed with an engine speed sensor and inputting the engine speed into a control unit. The engine speed is compared with a first predetermined engine speed. A first cleaning operation is conducted when the engine speed first exceeds the first predetermined engine speed following start-up. The engine speed is continued to be monitored and a second cleaning operation is conducted when the engine speed has exceeded a second predetermined engine speed and subsequently fallen below a third engine predetermined speed.
A further aspect of the present invention involves a method of operating an exhaust timing control valve control. The method comprises sensing an engine start-up and sensing an actual engine speed. The actual engine speed is compared to a first predetermined engine speed at which an electrical power generator is operable. An exhaust valve is closed according to a mapped strategy when the actual engine speed exceeds the first predetermined speed. The actual engine speed is compared to a second predetermined engine speed which is approximately an idle speed and a first exhaust valve cleaning operation is initiated when the actual engine speed first exceeds the second predetermined engine speed following engine start-up. The actual engine speed is then compared to a third predetermined engine speed that is approximately a speed at which it is desirable to open the exhaust valve. The exhaust valve is opened according to a mapped strategy when the actual engine speed exceeds the third predetermined engine speed. The actual engine speed is compared to a fourth predetermined engine speed that is above the second predetermined engine speed and below the third predetermined engine speed. A second exhaust valve cleaning operation is initiated when the actual engine speed decreases from at least the third predetermined engine speed to below the fourth predetermined engine speed. The actual engine speed is compared to a fifth predetermined engine speed that indicates an engine shutdown is occurring and the exhaust valve is opened when the actual engine speed decreases below the fifth predetermined engine speed.